1. Field of the Invention
This invention relates to picture image reading apparatus utilized in facsimile apparatus, a copying machine or the like, and more particularly to picture image reading apparatus capable of processing tones other than white and black.
2. Description of the Prior Art
In facsimile apparatus, a copying machine or the like, the following two methods have been used for reading a picture image depicted on a manuscript and then printing the read picture image on a recording paper. According to one method, the read picture image is identified as white and black picture images according to the tone or concentration of the picture image, the identified picture images are derived out as binary signals which are supplied to recording apparatus for recording read out picture images. According to another method, read out picture images are identified as picture images of multitones according to their tones, the identified picture images are derived as multivalue picture image signals which are supplied to a recording device for recording picture images including half tones between white and black.
In actual manuscripts, however, black characters of the picture images are often traced or underlined with red ink. Accordingly, according to the first method of deriving out binary picture image signals, as shown in FIG. 5a, where characters ABCD are written with black and characters EF are written with red, the characters EF will be recorded as black picture images just like the characters ABCD as shown in FIG. 5b so that it is impossible to represent characters EF in a different manner from the black characters.
According to a method wherein characters are derived as multivalue picture image signals, characters EF written with red ink will be recorded with a little lower tone or concentration than characters ABCD as shown in FIG. 5c, so that characters ABCD and EF can be discriminated in that they are depicted with different tones. However, since contamination and ground tone of the manuscript are also expressed as multivalue signals, noise appears in the recorded picture image, thus degrading the quality of the recorded picture images as shown in FIG. 5c.